Photodynamic therapy (PDT) is now recognized as an effective method for destroying abnormal tissue or tumors. To implement PDT, a photoreactive agent such as a hematoporphyrin is applied and is preferentially absorbed by the abnormal tissue, but to a much lesser extent by normal tissue. The photoreactive agent has a characteristic light absorption waveband. Light within this absorption waveband is administered to a treatment site where the abnormal tissue is disposed. The light activates the photoreactive agent, which destroys the abnormal tissue, but has much less effect on the surrounding normal tissue. However, it is common for the photoreactive agent to sensitize normal tissue, such as skin, for a period of time ranging, for example, from 48 hours to six weeks (depending upon the specific photoreactive agent administered), during which the patient should avoid exposure to sunlight or other bright light, since such exposure can damage the normal tissue.
It is also possible to treat subcutaneous primary and metastatic tumors with PDT using an external light source that emits light within a waveband that readily penetrates the cutaneous layer overlying the tumors. A principle drawback of using external light sources to administer the light therapy for either of these types of tumors is the effect that the therapy has on the surrounding normal skin, which is often photosensitive during the administration of the light therapy. Administering PDT with an external light source while the surrounding normal skin is affected by the photoreactive agent risks damage to the cutaneous layer, with possible risk of infection and increased risk of causing pain at the treatment site. While damage to the normal cutaneous tissue overlying a tumor is possible, it is preferable to minimize the area where such damage can occur.
A problem with administering light to an internal treatment site using a conventional external light source can arise if the internal tumor mass is asymmetrical. If light is administered from an external source through the overlying cutaneous layer, some portions of the tumor will likely receive too much light, and some portions will receive too little light to achieve an optimal result. It would be desirable to administer light to a cutaneous or subcutaneous treatment site for an extended period of time, and to limit the area over which the light is administered to the region of the treatment site. Thus, the patient should preferably be ambulatory during the treatment and not constrained to sit in a doctor's office while receiving the PDT. To facilitate therapy to any part of the body using an external light source, it is preferable for the light source to be fully portable and carried attached to the patient's body. Since many areas of the human body are non-planar and because a subdermal tumor can cause a substantial swelling of the cutaneous layers overlying the tumor, producing a convex lump on the skin, the light source should be able to conform to the shape of the treatment site by wrapping around such a non-planar surface and being adhesively secured in place.
Achieving a specific light dosimetry, i.e., the delivery of a desired intensity of light for a desired interval during PDT is another problem that is not properly addressed by prior art external light sources. An ambulatory external source of light suitable for administering prolonged, accurate illumination of irregular surfaces and capable of providing different light intensity to different regions of the treatment site is not known in the prior art. It will be evident that there is a clear need for such a device and a corresponding method for administering light therapy in this manner.